TW594082B - Compensating for chromatic dispersion in optical fibers - Google Patents

Abstract

An optical chromatic dispersion compensator (60) betters optical communication system performance. The dispersion compensator (60) includes a collimating means (61) that receives a spatially diverging beam of light from an end of an optical fiber (30). The collimating means (61) converts the spatially diverging beam into a mainly collimated beam that is emitted therefrom. An optical phaser (62) receives the mainly collimated beam from the collimating means (61) through an entrance window (63), and angularly disperses the beam in a banded pattern that is emitted from the optical phaser (61). A light-returning means (66) receives the angularly dispersed light and reflects it back through the optical phaser (62) to exit the optical phaser near the entrance window (63) thereof.

Description

说明 Description of invention:

[Technical Field of the Invention Family J Field of the Invention This application declares the benefit of US Patent Application No. 60 / 396,321, filed on July 16, 2002. The present invention relates generally to the technical field of optical fiber communications, and in particular, to compensation for accumulated dispersion when light is transmitted through optical fibers of a communication system. BACKGROUND OF THE INVENTION The increasing demand for low cost bandwidth in optical fiber communication systems provides an incentive for increasing the bit rate / transmission distance and the number of wavelength division multiplexed (WDM) channels carried by optical fibers. The main limiting factor in high-bit-rate, long-distance optical communication systems is the dispersion that occurs when optical propagation through optical fibers. Dispersion causes light waves of a specific wavelength to pass through the optical fiber at a speed different from the speed at which light of different wavelengths travels. The effect of dispersion is that optical pulses containing multiple wavelength components become severely distorted after running through long optical fibers. The distortion of the optical pulse will reduce the quality and miss the information carried by the optical signal. The dispersion characteristics of optical fibers have two parameters: 1. Group velocity dispersion (GVD), which is the ratio of the group velocity change to the wavelength; and 2. Dispersion slope, which is the ratio of the dispersion change to the wavelength. For a typical optical fiber communication system that carries light over a wide range of wavelengths (such as a WDM system or a system with direct modulation laser or Fabry_p coffee laser = =.) The slope is necessary. 1. In recent years, several different types of optical fibers exhibiting different dispersion characteristics have been used to assemble optical fibers. The dispersion characteristics exhibited by these different types of optical fibers depend on the length of the optical fiber and the optical fiber. = And how optical fibers are manufactured, and the assembly of optical fibers depends on other environmental conditions. Therefore, in order to compensate for the dispersion exhibited by these irrelevant optical fibers, the rest has single-type dispersion compensation devices, which provide Variable GVD and dispersion ramp simplify the storage system and optical communication network management. Several solutions have been proposed to mitigate dispersion in optical fiber communication systems. The technique used to compensate for the dispersion that is unintentionally shown in Figure 1A is in line with the usual The transmission optical fiber 30 is inserted in series with a relatively short special dispersion compensation optical fiber (DCF) 3 and the DCF 31 has a special The plane index profile shows a dispersion opposite to that of the optical fiber 30. In this way, the light transmitted through the optical fiber 30 is subjected to the dispersive light to propagate through the DCF 31, which eliminates the dispersion caused by the transmission through the optical fiber 30. However, In order to obtain the dispersion opposite to the optical fiber 30, the DCF 31 has a much smaller modal field diameter than the optical fiber 30, and the DCF 31 is more susceptible to nonlinear effects. In addition, it is difficult to use the DCF in the lowest space modal operation 31 to completely eliminate the GVD and dispersion slope exhibited by two special optical fibers, namely dispersive displacement optical fiber (DSF) and non-zero dispersive displacement optical fiber (NZDF). Figure 1B schematically shows an alternative line Internal dispersion compensation technology is inserted into a first modal converter 33, which receives light propagating between the first optical fiber 30 and a high-modal DCF 34 through a section of the optical fiber 30. After passing through the high-modal DCF 34 The light passes through a second modal converter 35 and enters the second-stage optical fiber 30. Similar to the DCF 31 in FIG. 1A, the high-modal DCF 34 exhibits a dispersion opposite to that of the optical fiber 30. Supports a single higher-order spatial mode than that supported by dCf 31. The modal field diameter of the higher-mode DCF 34 of the higher-order spatial mode can be compared to two optical fibers 30. Therefore, the mode converter 33 The light radiated by the first optical fiber 30 is transformed into a higher-order spatial mode supported by the high-modal DCF 34, and the mode converter 35 reverses the radiation from the higher-order spatial mode emitted by the chirped mode DCF 34. Transforming the returned light into a lower-order space plate is used for light closing back into the second optical fiber 30. The problem shown by the device shown in Figure 1B is that it is difficult to completely convert light from a spatial mode into Another problem is that it is also difficult to maintain light running in a single higher-order spatial mode. Therefore, the integrity of the signal compensated for dispersion by the device shown in Figure 1B is susceptible to model dispersion due to different group velocities of light traveling in multiple different spatial modes. Due to the difficulty of mediating DCF in the modalities of various optical fiber 30 types in the art, it is impractical to adjust the dispersion exhibited by DCF to the specific optical fiber 30. In addition, DCF also exhibits high insertion loss. This loss of optical signal strength must be compensated with an optical amplifier. As a result, the use of DCF to compensate for dispersion significantly increases the overall cost of the optical communication system. Figure 2 unintentionally shows that different technologies use dynamic translation (also fiber Bragg grating 42 to provide dispersion compensation. The different wavelength components of the 594082 line pulse emitted by the optical fiber 30 are emitted into the dynamic translation grating through a circulator 41. 42 so that different sections of the dynamic translation grating 42 are reflected back towards the circulator 41. A carefully designed dynamic translation grating 42 can thus compensate for the dispersion accumulated in the optical fiber 30. The amount of dispersion provided by the dynamic translation grating 42 is 5 It can be adjusted by changing the tension and / or temperature of the grating fiber. Unfortunately, Bragg gratings only reflect narrow bandwidth WDM spectra. Multiple dynamic translation gratings can be cascaded to extend the spectral width. However, cascade multiple The dynamic translation grating 42 will cause the result of an expensive dispersion compensation device. Figure 3A schematically shows another technique, which is a dispersion compensation application body 10 diffraction grating 50. Specifically, the light leaving the transmission optical fiber 30 is first Is formed as a collimated beam 51. The volume diffraction grating 50 is then used to generate an angular dispersion (diffraction) from the collimated beam 51 A ratio of the change in wavelength). A light returning facility 52, which typically consists of a lens 53 and a mirror 54 behind it, is placed on the focal plane of the lens 53 and reflects the diffracted light back to the 15 diffraction grating 50. The diffracted light is reflected back to the diffraction grating 50 to transform the angular dispersion into dispersion. A circulator inserted along the calibration beam path can be used to separate the dispersion of the incoming calibration beam 51 leaving the diffraction grating 50 Compensated light. In the device shown in Figure 3A, the amount of dispersion can be adjusted by changing the distance between the diffraction grating 50 and the lens 53, and / or the curvature of the beam folding mirror 54. However, the body Diffraction grating 50 produces only a small angular dispersion. As a consequence, the use of the device shown in Figure 3A to compensate for the large dispersion occurring in an optical communication system would require an impractical device. An analog calibration technique such as in 2002 5 U.S. Patent No. 8 594082 6,390,633 (referred to as the coffee patent) issued to Masataka Shirasaki and Simon Cao on May 21, entitled "〇ptical Apparatus

Which Uses a Virtually Imaged Phased Array to Produce Chromatic Dispersion "replaces the diffraction grating 50. As shown in Figure 3B of Figure 7 of Figure 633, which is reproduced, VIPA includes A linear focusing element such as a cylindrical lens 54 and a specially painted parallel plate 58. The collimated beam 51 passes through the linear focusing cylindrical lens 57 and enters VIPA at a small angle of incidence, and emerges from VIPA at a large angle. In FIG. 3A With the combination of displayed light return facility 52, VIPA can generate sufficient dispersion to compensate for the dispersion that occurs in the optical fiber transmission system. Unfortunately, 10 VIPA allocates the energy of the calibration beam 51 as multiple diffraction orders. The emission order exhibits different dispersion characteristics, and only the first order can be used to compensate for dispersion. As a consequence, VIPA exhibits high optical loss, and makes vivIPA's implementation of dispersion slope compensation complicated and expensive. VIPA also leads to high dispersion waves, That is, for the rapid change in the residual dispersion of the wavelength, this makes VIPA unsuitable for in-line dispersion15 compensation.

Another technique that can be used for dispersion compensation is an all-pass filter. An all-pass filter is a device that exhibits flat radiant response and periodic phase response to incoming optical signals. Since dispersion is the second derivative of phase delay, as known to those skilled in the art, an all-pass filter can be used to compensate for dispersion. All 20-pass filter The application of the all-pass filter for dispersion compensation is Gires-Toumois interferometer and ring mirror. An article in mEE 1998

Photonic Technology Letters, Volume 10, Issue 7, page 944 An article by C. Madsen and G. Lenz entitled "〇pticai All-Pass Filter for

Phase Response with Applications for Dispersion 9

The "Compensation" article reveals how an all-pass filter can be used for dispersion compensation. Problems with an all-pass filter using dispersion compensation include its introduction of high dispersion waves, or the inability to generate sufficient dispersion compensation for practical applications. The consequences are, All-pass filters and wave filters are not suitable for in-line dispersion compensation. Because dispersion compensation is very important in high-performance optical fiber communication systems, it has a low dispersion wave pattern, a relatively low insertion loss, and it can compensate for transmission in optical fibers. The simple and adjustable dispersion compensator exhibited by the various types of optical fibers that have been deployed in the system. The simple and adjustable dispersion compensators are both highly efficient in terms of increasing the bit rate / transmission distance and the WDM channels that the optical fibers can carry. Advantageous. [Summary of the Invention 3 Summary of the Invention The present invention provides a method and a device that produce an adjustable amount of dispersion and is practical for compensating the dispersion of an optical fiber system. The object of the present invention is to provide a low dispersion Waveform dispersion compensation. Another object of the present invention is to provide dispersion compensation that exhibits relatively low insertion loss. Another object of the present invention is to provide practical dispersion compensation. The other object of the present invention is to provide dispersion compensation, which can compensate for various types of optical fibers that have been deployed in the optical fiber transmission system or can be deployed in the future. Various types of dispersion shown. Ft Ming another-the goal is to provide dispersion compensation, which increases the bit rate / input distance. Wei Neng Cheng = M; r. Color coding is fine, which increases the optical fiber G: and: =: The goal is to provide dispersion compensation, which simultaneously compensates the three heads of broadcast, rain, and month. ^ To provide dispersion compensation, which simultaneously compensates the GVD and dispersion slope of the entire range of transmission through-optical fiber. To non = Mingzhi another-target To provide dispersion compensation, it is less susceptible to non-linear effects. 10

The other issue of this month is to provide dispersion compensation, which does not need to change the light between different spatial modes. Another goal of this month is to provide dispersion compensation, which is less susceptible to the effects of model dispersion. This is another thing-the goal is to provide dispersion compensation, which takes up a relatively small amount of space. 15 Beyond the Tree—The goal is to provide cost for M optical trajectories

Effective dispersion compensation. Briefly, the present invention is a dispersion compensator and a method of operating the same which is used for better performance of an optical communication system. In a preferred embodiment, the dispersion compensator includes a calibration facility that receives a spatially divergent beam of light from the end of an optical fiber. The calibration facility transforms the spatially divergent light beam into the main collimated light beam that is emitted thereby. The dispersion compensator also includes an optical phase effector that provides an entrance window to receive the predominantly collimated light beam. The optical phase effector will be angularly dispersed by the 11 594082 optical phase effector which is radiated into a band model. In this mode, the light beam received by the optical phase effector is separated into wavelength bands, so that light with a specific frequency in a specific band is deviated angularly from light with other frequencies in the same band. 5 Finally, the dispersion compensator includes a light return facility that receives the angularly dispersed light and reflects it back through the optical phase effect to leave the optical phase effect near its entrance window. These and other features, objectives, and advantages will be understood by or understood by those skilled in the art from the detailed description of the following preferred embodiments, such as the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a schematic diagram showing a conventional technique for dispersion compensation, which uses a special dispersion compensation optical fiber to reduce the dispersion of an optical communication system; FIG. 1B is a schematic diagram that discloses The conventional technique of dispersion compensation uses a modal converter and a high-modal dispersion compensation optical fiber to reduce the dispersion of an optical communication system. FIG. 2 is a schematic diagram showing a conventional technique for dispersion compensation. A fiber Bragg grating is used to reduce the dispersion of an optical communication system; Figure 3A is a schematic diagram showing a conventional technique for dispersion compensation, which uses a volume diffraction grating and light return facilities to reduce the dispersion of an optical communication system; FIG. 3B is a schematic diagram illustrating a conventional technique for dispersion compensation, which uses VIPA to generate the required large-angle dispersion to reduce the dispersion of an optical communication system 12 594082. FIG. 4 is a schematic diagram illustrating a method according to the present invention. An embodiment of a dispersion compensation device, which includes a light facility, an optical phase effect device, and a light return facility; 5 FIG. 5A A schematic view showing a plan view of a prism based on the light coupling facility shown in FIG. 4 of an embodiment of the present invention; FIG. 5B is a schematic view showing the light surface combination shown in FIG. 4 of another embodiment of the present invention A plan view of a facility-based volume diffraction grating; Figure 6A is a schematic diagram that reveals that VIpA, a conventional technique, is a diffraction model of a single 10-wavelength light beam; Figure 6B is a schematic diagram that reveals The optical phase effect device according to the present invention is a diffraction model in which a light beam with a single wavelength is generated; Figures 7A '7B' 7C '7D' 7E and 7F are schematic diagrams showing various different combinations, all of which are used in accordance with the present invention An exemplary embodiment of an optical phase effector is shown in FIG. 8A is a schematic view illustrating an embodiment of the present invention, in which the light return facility uses a concave mirror as its light focusing element; FIG. 8B shows a view directed to the present invention —The position of the light focusing element and the light returning lens of the optical phase effector according to the embodiment; the front view is a schematic plan view showing that Method for returning the light of which M dispersion has been compensated to a communication system; FIG. 9B is a plan view showing a method for consuming the light whose dispersion has been compensated and returning to a communication system according to an embodiment of the present invention. An alternative method; 13

Fig. 10 is a schematic diagram showing the intensity distribution of the light beams containing multiple WDM channels when the light is returned to the mirror using the 4,8A # 9A5 | l embodiment of the present invention; Fig. 11® is a schematic diagram Reveal the various shapes of the light-sending mirrors according to Figure 4 of the present invention, which fully compensate for the chromatic dispersion exhibited by the optical fibers available in various markets; and Figure 12 is an eye diagram showing the distance away from the According to the section of 80 km of optical fiber, the simulation result of the 10 Gbps optical fiber transmission system containing 4000 km of optical fiber compensated by the dispersion compensator of the present invention. T] Detailed description of the preferred embodiment FIG. 4 shows According to an optical dispersion compensator according to the present invention, the whole is represented by the symbol # ϋ6 (). In the embodiment, the dispersion compensation H6G includes basic components, a calibration facility 61, an optical phase effector 62, and a The light is sent back again and again. The optical phase effector 62, which will be explained in more detail below, includes an entrance window 63 and two parallel surfaces 64, 65. The light return facility 66, which is also explained in more detail below, includes— Light gathering The element 67 and a curved mirror 68 are located near the focusing plane of the ray focusing element 67. As shown in FIG. 5A, the calibration facility 61—the preferred embodiment includes a collimator 71, which receives optical fiber 3. The spatially divergent light beams at the ends are radiated. As understood by those skilled in the art, the button radiated by the end of the optical fiber% can be irradiated in two mutually orthogonal planes due to the passage of light through the optical_3 (). The collimator 71 transforms the spatially divergent light beam emitted from the end of the optical fiber 3 () into a calibration beam 72, which retains two mutually orthogonal polarizations when radiated into the free space by the collimator 14 594082. The calibration beam 72 impinges on the birefringent plate 73, which separates the incoming calibration beam into two spatially identifiable components with a straightened polarization 74, 75. Then the light with the polarization 74 passes through the -first-half wave Plate 76, which rotates this light, so that the 5 polarizations of the two beams are located on the same surface, and the two beams, which now all have polarizations on the same surface, impinge on 稜鏡 77, which disperses the two beams at a slight angle. Wait at a slight angle The scattered two beams impinge on a second half-wave plate 78, which rotates the polarization of the two beams by 90. An alternative embodiment of the calibration facility 61 shown in Figure 5B is replaced by a one-way diffraction grating 77 &稜鏡 77 to obtain a similar amount of angular dispersion. An alternative embodiment of this calibration facility 61 including a body diffraction grating 77a omits the second half-wave plate 78. Whether the calibration facility 61 uses 稜鏡 77 or body wrap The grating 77a and the calibration facility 61 emit 15 beams of mainly collimated light as discussed in more detail below. It should be noted that dispersion compensation and dispersion slope control in optical transport systems are not critical, as in In a system involving a wavelength-limited or relatively short optical fiber 30, chirp 77 or a volume diffraction grating 77a may have very little effect on the dispersion compensator 60. In addition, those skilled in the art will understand that if the light leaving the optical fiber 30 has a well-defined polarization, for example, if the light is directly from a laser or other type of device that maintains a single, flat polarization, The optical configurations shown in Figures 5A and 5B, respectively, can be significantly simplified. The emitted light from the self-calibration facility 61 enters the optical phase effect 62 through the entrance window 63 and will be reflected back and forth between parallel surfaces 15 594082 64, 65 along the length of the optical phase effect 62. In the subordinate and secret arbitrarily-matched I, — the calibration setting Γ ’— —. Since === _ 62 internally strikes the surface 65 close to the critical corner, the number of surfaces from the surface _ 65 is also missing any coating. Shooting, as used in # 面 户 地 光 Γ communication system, the optical phase effector 62 is a solid board, although it can also be made of any other material, 10 15 1 · is transparent to allow light to propagate through , Shi Tuyu and bit effect 62; and 2. has a refractive index greater than the surrounding media. The second phase a of the optical phase effector 62, and one of the surfaces of the ancient death ten, the surface 64 is preferably coated with a reflective film, for example, E a J, such as the wavelength of the light impinging on it 98% reflective film. As a consequence, surface 64 is referred to herein as a "reflective surface." In addition, the surface 65 is preferably polished, although it may also be coated with partially anti-pure layers, such as a film having approximately 98% reflectivity at the wavelength of the light impinging thereon. This surface is referred to herein as "diffracting surface i. One corner of the solid-state optical phase effector 62 constituting the entrance window 63 is beveled. The beveled entrance window 63 is coated with an anti-reflective film to promote the beam Enter here into the optical phase effector 62. After the light beam passes through the entrance window 63 and enters the entrance window 63 at a nearly normal incident angle, it is divided into two parts, which successively hit the diffuse refracting surface 65 of the optical phase effector 62. As explained above, 'Most of each beam is reflected inside the optical phase 16 when it hits the surface 65. 594082 The effector 62 reflects. The portion of each beam that is not reflected by the surface 65 leaves the optical phase by refraction through the surface 65 Effector 62. The combination of the optical phase effector 62 preferably aligns each light beam striking the surface 65 to an incident angle 0, which is slightly smaller than the critical angle. As a consequence, the optical phase effector 5 62 The meaning of the group is that the refraction of light on the surface 65 is greater than that by the refracted surface 65

The normal line occurs near the critical p at an angle p of 45 °. The part of each light beam reflected on the surface 65 continues to be reflected back and forth between two parallel surfaces 64, 65 of the optical phase effector 62, and a part of the light beam hits the surface 65 and is refracted by the optical phase effector 62. Every time the light beam encounters the astigmatism 10 surface 65, a small portion of the light beam leaves the optical phase effector 62 with refraction. If the optical path has a delay between successive reflections, that is to say, the constructive interference occurring between all the beams emerging from the surface 65 is equal to an integer multiple of the wavelength λ of the light entering the optical phase effector 62. Δ p = 2hn cos Θ = m λ ⑴ 15 4h2 (n2-sin2 (/)) = m2 λ2 此处 here

η is the refractive index of the material forming the optical phase effector 62, 0 is the angle of incidence of the light reflected by the optical phase effector 62 on the surface 65, and is the refraction angle of the light passing through the surface 65 and leaving the optical phase effector 62. The angular dispersion capability of the optical phase effector 62 established for the thickness m of the optical phase effector 62 by the order of interference is derived from the following relationship (3): 17 5594082 δ φ n2 — sm2φ-^- ⑶ δ λ λ sin ψ cos φ If P is close to the critical angle, the optical phase effector 62 generates a large angular dispersion of the light transmitted through the surface 65. If ρ approaches the normal to the surface 65 of the optical phase effector 62, large angular dispersion can also be achieved. The direction of the light emitted from the surface 65 corresponds to the direction of the light emitted from the parallel plate 58 of VIPA. 10 Although the optical phase effector 62 has similar angular dispersion capabilities as VIPA, its diffraction patterns are significantly different. As shown schematically in FIG. 6A, the light beam at the waist of the parallel plate 58 of VIPA must be very small to reduce the angle P and the loss of light energy in synchronization. The consequence is that for a specific wavelength of light; ^, the narrow beam at the waist of the parallel plate 58 of VIPA produces a large angle 15 of the refracted beam. In other words, the energy of the light diffracted by VIPA is distributed to multiple orders. Due to the different diffraction properties of beams of different orders, as mentioned earlier in VIPA, only one diffraction order is used for dispersion compensation. As a consequence, VIPA is essentially a high-loss device. Alternatively, the beam width in the optical phase effector 62 is similar to the thickness h of the optical phase effector 62. The wide beam width in this optical phase effector 62 20 causes the light energy of the light refracted at the surface 65 to be concentrated as shown schematically in FIG. 6B for any one beam of a specific wavelength at a single order. In order to compensate for the dispersion in an optical communication system containing multiple WDM channels, Jia Jiayi designed the incident angle of the light beam 25 in the optical phase effector 62 according to the following formula (4): 0: c cos 0 2 ---- 2hAfn (4) 18 C is the speed of light Δ f is the frequency separation between adjacent WDN channels. Note that the refractive index n of the optical phase effector 62 depends on the wavelength. The angle of incidence 0 thus varies with wavelength. In particular, with respect to the light entering i for each WDM channel, there exists a specific incident angle 0i. The angular dispersion of the light beam in the optical phase effector 62 is facilitated by angular dispersion generated by the 稜鏡 77 of the calibration facility 61 or the volume diffraction grating 77a. If the incident angle 0 is close to the angle of the total internal reflection as in the present preferred embodiment, the optical phase effector 62 not only generates a large angular dispersion at a specific wavelength as shown in the relationship (3), but the optical phase effector 62 also magnifies and calibrates. Corner of facility 61 is scattered. Angular dispersion magnification provides a way to reduce dispersion patterns. In order to reduce the knowledge of the light entering the optical phase effector 62 from the calibration facility 61 and also preferably any particular wavelength of the light ^ around the pattern leaving the surface 65 of the optical phase effector 62-the light beam is only produced- It may be that the angular dispersion generated by the calibration facility 61 is h, that is, the beam emitted by the calibration facility 61 < calibration is difficult according to the following Φ relationship (5) has a beam waist W on the plane of the plate perpendicular to the parallel plane 65. · W〇 ^ hsin θ Here (5) h is the thickness of the optical phase effector 62. The optical phase effect 1162 is internal to the surface 65 of the reflected light. The above relationship (5) is calibrated by the calibration facility 61. The beam ensures that the energy of the main collimated beam that hits the entrance _ 63 is more than 50%. It is diffracted into a beam of any wavelength with a specific wavelength that is scattered by the angle emitted by the optical phase effector 62. The pattern becomes a diffraction smaller than the third order. 5 Alternative embodiments of the optical phase effector 62 are shown in Figures 7Λ to 7F. In these alternative embodiments of the optical phase effector 62, the entrance window 63 may be a chamfered surface shown in Fig. 4, or a projection 82 extending from one of the parallel surfaces 64, 65 as shown in Figs. 70-7. Be formed. The light entering the entrance window 63 of the 稜鏡 82 is reflected inside the 稜鏡 10 82 before first striking one of the parallel surfaces 64 or 65. As shown for various alternative embodiments, the reflective surface 64 may be coated with a highly reflective film or be partially transparent. If the surface 64 is partially transparent, the 'optical phase effector 62 exhibits a large optical loss. However, for such an assembly of the optical phase effector 62, light leaked from the surface 64 can be used for performance monitoring. It should be noted that if the reflectivity of the parallel surfaces 15 64, 65 is made independent of polarization with a special optical coating, the calibration facility 61 is used for the light impinging on the entrance window 63 of the optical phase effector 62. The resulting polarization control is unnecessary. As previously described, the preferred embodiment of the light returning facility 66 includes a light focusing element 67 and a curved mirror 68 placed near the focal plane of the light focusing element 67. The light focusing element 67 may be a lens as indicated in FIG. 4. Alternatively, as shown in Fig. 8A, the concave mirror can also be used as a light focusing element 67 in a folded type assembly for light returning facilities. The light focusing element 67 is preferably located along the direction of the diffracted light beam radiated from the surface 65 of the optical phase effector 62, and the distance from the surface 65 is approximately a focal distance as shown in FIG. 8B, that is, the light is focused by 20 594082 lines. 70 pieces of 67 f. In the preferred embodiment of the light return facility 66, the light beams appearing from the surface M of the optical phase effect Γ are collected by the light focusing element 67 so as to be projected onto a curved mirror near the focal plane of the light focusing element 67. The light beam reflected by the 5-curved mirror 68 is transmitted back to the facility through the light, and the optical phase effector 62 reverses its track to exit through the entrance window 63 and advances through the calibrator 71 of the calibration facility 61. Preferably, as shown in the plan view of Figure 9A, through calibration! The light coming back from | 71 can be isolated from the light space that enters by slightly tilting the light focusing element 67 perpendicular to the plane of symmetry of the dispersion compensator 60. Alternatively, as shown by the 9th Baj, the light transmitted back through the calibrator 71 longitudinally may be isolated by the circulator% and the light entering the calibrator 71. Although FIG. 9B shows that the circulator 86 is located between the optical fiber 30 and the weight facility 61, the circulator 86 is alternatively inserted between the calibration facility 61 and the optical phase effector 62. 15 The dispersion cold produced by the dispersion compensator 60 follows the relationship (6): n 2 (n2-l) 〒 〇 ^ — c λ Rcos2 φ (6) 2〇 Here R is the curvature radius of the curved mirror 68 Note R is defined as positive for a convex mirror and negative for a concave mirror. In terms of fixed diffraction and fixed focal length f, the relationship ⑹ indicates that the dispersion produced by the dispersion compensation ^ H6G is directly proportional to the curvature of the curved mirror 特别. In particular, S 'adjusts the curvature of the curved mirror 68, so that The special wavelength of the light is complete. The dispersion of the fixed wire transmission can always be 21 25 594082. Furthermore, the 'small angle dispersion introduced by the 准 77 of the parent quasi facility 61 or the volume diffraction grating 77a A band-forming pattern is generated which angularly disperses light beams of different wavelengths appearing on the surface 65 of the optical phase effect device 62. That is, the optical phase effector 62 diffracts 10 light rays having different wavelengths at slightly different angles WDMSg. Moreover, light with a special frequency in each specific band of the band-forming pattern is angularly deviated from light with other frequencies in the same band. Also, the angle generated by the optical phase effector 62 The f-shaped wave of the scattered light exhibits an angular rate of change for the center frequency in a particular band. Its angular rate of change for the center frequency in other bands is different. The consequences are as shown in Figure K). As shown, the light focusing element Yang-WDM channel rays project this waveband type to a curved mirror 6 8 located at the focal plane of the focal plane of the light focusing element 6 7. The curvature of the right curved mirror 68 has The entire focal point 15 20 plane of the element 67 will change. The projection of the waveband pattern by the light focusing element 67 to different positions of the curved mirror 68 can be advantageously developed. The use of curved mirrors with a suitably varying curvature allows dispersion compensation. All WDM channels propagating through the optical fiber 30 are compensated simultaneously. Figure u shows the curved mirror of the exemplary embodiment of the dispersion compensator 60_ a preferred shape, which is one of the commercially available optical fibers 30 Various incomplete formulas completely compensate wd and dispersion slope. In an exemplary embodiment of the dispersion compensator 60, the optical phase effector 62 is made of a thick mmm cutting plate. According to the optical phase shown in 7A_ ^ Various embodiments H63 of the effector 62 are formed on the outer surface of the board. The reflective surface 64 has a gold coating, and the diffuse refracting surface 65 22 594082 is polished. The light beam in the optical phase effector 62 is incident The angle 0 is about 16. And the focal length of the light focusing element 67 is about 100 mm. The light focusing element of the present invention provides several advantages and features compared to the existing dispersion compensation device. First, the color compensation complements 60, which contributes to GVD and 60. Independent control of both the dispersion slope. Specifically, for any optical fiber 30 of a specific length, its GVD can be compensated by the proper curvature of the folded curved mirror 68, and its dispersion slope can be compensated by the same folded curved mirror. The appropriate curvature variation of 68 is compensated. First, the almost calibrated light beam in the optical phase effector 62 will be the energy of the diffracted light rays to a few diffractions 1¾ at a specific 10 wavelength, forming a wide Bandpass width with minimal yield loss. For example, the color filter 60 of the present invention exhibits a 0.5 dB bandwidth greater than 40 GHz for a WDM system having adjacent channels separated by ioogHz. Secondly, according to the relationship (6), the gvd and dispersion 15 produced by the dispersion compensator 60 change linearly with the curvature of the folded curved mirror 68. Therefore, the shape of the curved mirror 68 that provides the full GVD and dispersion slope compensation for the optical system is determined solely by the shape of the optical fiber 30 and changes linearly with the length of the optical fiber 30. Therefore, in Fig. U, the vertical axis related to the graph display of the various curvatures of the different curved mirrors 68 is normalized to the length of the various optical fibers. Fourth, the dispersion compensator 60 can be designed with a minimum dispersion slope, for example, by setting the radius of the folded curved mirror 68 according to the following relationship:

Rcos2 φ = constant Φ double (7) According to the relationship, the dispersion compensator 6 equipped with the curved mirror 68 is useful in compensating optical 23 594082 communication systems. Here: The wavelength of L light is unstable, such as From an uncooled laser; or 2. The spectrum of this light is very broad ', such as from a directly modulated laser. Finally, the dispersion compensator 60 introduces a small dispersion of the light rays propagating through the optical communication system. Therefore, the dispersion compensator 60 can be used for terminal dispersion compensation and in-line dispersion compensation for long-distance optical fiber systems. For in-line dispersion compensation of long-return optical fiber systems, several dispersion compensators 60 are installed at spaced locations along the 30-fiber optical fiber. For example, Fig. 12 shows an eye diagram result of simulating a 10 Gbps optical fiber transmission system 10 containing 4000 km of optical fibers to compensate with a dispersion compensator 60 every 80 km along the optical fibers 30. For those skilled in the art, it is clear that the quality degradation due to dispersion shown in Figure 12 is very small. Although the present invention has been described with reference to the presently preferred embodiment, it will be understood that the disclosure is purely illustrative and is not to be construed as limiting. For example, the color compensator 60 embodiment described above is preferably A chirped or volume-diffractive grating 77a is included to provide angular dispersion of the light radiated from the calibration facility 01 and impinging on the entrance window 63. However, it is not intended that the dispersion compensator 60 must include this corner dispersion element 2 in order to be included in the following patent application scope. As mentioned above, in the application of the dispersion compensation 20 of the dispersion slope of the towel, the nearly calibrated beam of light is generated by the homozygous optical fiber 30 and the optical phase effect device at an efficiency of 100%. Any type of modal light coupler can be used as the calibration facility. This side coupler can be only a standard optical calibrator. _ As described above, the entrance window 63 of the optical phase effector 62 is preferably coated with a film that resists 24 594082 reflection. However, it is not intended that the dispersion compensator 60 must have such coating in order to be included in the scope of the following patent applications. The only requirement is that the entrance window 63 of the optical phase effector 62 is simply partially transparent to the wavelength of the light impinging on it. 5 In the above embodiment of the present invention, the birefringent plate 73 and the half-wave plates 76 and 78 will receive the light beams from the optical fiber 30 before they will be properly polarized by the 稜鏡 77 and the optical phase effector 62. Linearly polarized to be dispersed at an angle. However, it is not intended that the dispersion compensator 60 be contained in the following patent applications, which is limited to the use of these specific polarizing elements. Instead of 10, the dispersion compensator 60 only requires a suitably polarized light beam that hits the entrance window 63 of the optical phase effector 62. Further, as described above, the parallel surfaces 64, 65 of the optical phase effector 62 may be coated with a thin film so that the corresponding reflectivity is insensitive to the polarization of the light beam. If such coatings are applied to parallel surfaces 64, 65, the polarization of the light beam striking 15 to the entrance window 63 need not be controlled, and such as the polarization control elements of birefringent plates 73 and half-wave plates 76, 78 Can be cancelled in the calibration facility 61. By analogy, to improve optical efficiency, anti-reflection coating may be advantageously applied to the light focusing element 67 to reduce the loss of light passing through a lens. For optical effectiveness, it is also advantageous if the curved mirror 68 has a highly reflective coating. As described above, the preferred interval between the surface 65 of the optical phase effector 62 and the light focusing element 67 is equal to the focal length f of the light focusing element 67. However, the dispersion compensator 60 encompassed by the scope of the following patent applications is not limited to this particular geometry. Instead, the distance between the focusing element 66 and the surface 25 594082 64 of the optical phase effector 62 may be set to any value. As described in more detail below, this distance is actually even adjustable. -Generally speaking, the dispersion produced by the present invention is related to its geometry as follows: 5 f2 j3 cc (f — u--) R (8) Here, U is defined by the surface 65 of the optical phase effector 62 The distance f between the optical axis of the light focusing element 10 67 and the light focusing element 67 is the focal distance R of the light focusing element 67 is the radius of curvature of the Zigong curve lens 68. The adjustable dispersion dispersion compensator 60 according to the present invention can be adjusted by u or or u and R are rounded by β. As far as the adjustment of u is concerned, the preferred embodiment of the dispersion compensator is to send the light back to the facility 6 as shown by the arrow in Fig. 4 and place it on the translation port. Alternatively, the curved mirror is made with an adjustable curvature. There are many ways to make the curvature of the curved mirror 68 adjustable. -One method is to apply an elastic bending force to the curved 20 mirror 68 in the direction indicated by arrow 70 in Fig. 4. This bending force can be generated mechanically, such as pushing a screw. If the mirror is made of a bimetal material, the curvature of the curved mirror 68 can also be adjusted thermally. The optimum mirror shape can be achieved by making the curved mirror 68 with varying rigidity, by applying f-curving force to multiple positions of the curved mirror 68, or by a combination of these two techniques. The curved mirror 68 with uneven sentence curvature, which is located near the focal plane of the light focusing element 25, is translated horizontally to its optical axis, that is, it is translated along the focal plane of the light focusing element 67, and the curved mirror 26 is adjusted. 26 594082 Of curvature. The curvature of the curved mirror 68 can also be adjusted by replacing the curved mirror 68 having a specific shape with another curved mirror having a different shape. As a consequence, without departing from the spirit and field of the present invention, various changes, modifications, and / or alternative applications of the present invention will undoubtedly be recommended to those skilled in the art who have read the previous disclosures. Therefore, it is intended that the scope of the following application patents be interpreted as inclusive of all changes, modifications, or alternative applications as falling within the true spirit and field of the present invention. [Brief description of the figure] Figure 1A is a schematic diagram showing the conventional technology for dispersion compensation. 10 It uses a special dispersion compensation optical fiber to reduce an optical communication system. Figure 1B is a schematic diagram showing the dispersion for dispersion. Compensation is a conventional technique that uses a modal converter and a high-modal dispersion compensation optical fiber to reduce the dispersion of an optical communication system; a 15

Figure 2 is a schematic diagram 'revealing conventional techniques for dispersion compensation, 1 reducing L & agg gratings—dispersion of optical communication systems;

Figure 3A is a schematic diagram 'revealing the optical performance of the volume diffraction grating used for dispersion compensation, self-rafting, dispersion; H-line facility reduction-20 of the optical communication system Figure 3B is a schematic diagram of its use VIPA is used to generate the required dispersion; reveal the conventional technology for dispersion compensation, the large-angle dispersion reduction-optical communication system Figure 4 is a schematic diagram, which discloses an embodiment according to the present invention, including- The device first sighs, an optical phase effect device, and a 27 594082 light return facility; Figure 5A is a schematic diagram showing the light coupling facility based on the light coupling facility shown in Figure 4 of an embodiment of the present invention Plan view; FIG. 5B is a schematic view showing a plan view of a volume diffraction grating based on the light-coupling facility shown in FIG. 45 of another embodiment of the present invention; and FIG. 6A is a schematic view showing a conventional technique. VIPA is a diffraction model of a light beam having a single wavelength; FIG. 6B is a schematic diagram showing a diffraction model of a light beam having a single wavelength using the optical phase effector according to the present invention 10 Figures 7A, 7B, 7C, 7D, 7E and 7F are schematic diagrams illustrating various exemplary combinations, all of which are used in an exemplary embodiment of an optical phase effect device according to the present invention; Figure 8A is a schematic diagram that reveals An embodiment of the present invention, wherein the light-return facility uses a concave mirror as its light-focusing element; FIG. 8B shows the position of the light-focusing element and the light-returning mirror of the optical phase effector according to an embodiment of the present invention; FIG. 9A is a schematic plan view showing a method for combining the light whose dispersion has been compensated to return to a communication system according to an embodiment of the present invention; FIG. 9B is a schematic plan view showing a method according to an embodiment of the present invention 20 An alternative method for coupling the light whose dispersion has been compensated back into a communication system; FIG. 10 is a schematic diagram showing the use of the 4, 8A and 9A images of the embodiment of the present invention when the light is returned to the mirror Intensity distribution of light beams coming from multiple WDM channels; 28 594082 Figure 11 is a schematic diagram showing the different shapes of the light returning to the mirror according to Figure 4 of the present invention. Full compensation for the dispersion exhibited by various types of optical fiber available on the market; and Figure 12 is an eye diagram showing the distance of 4000 km which is compensated by the dispersion compensator according to the present invention, which is 80 km away from the segment of optical fiber. Simulation results of a 10 Gbps optical fiber transmission system, one of the optical fibers. [Representative symbols for the main components of the drawing] 30 ... optical fiber 64 ... parallel surface 3l ... dispersion dispersion optical fiber, DCF 65 ... parallel surface 33 ... modal converter 66 ... light return facility 34 ... high modal DCF 67 ... light focusing element 35 ... modal converter 68 ... curved mirror 4l ... circulator 69 ... arrow 42. " Bragg grating 70 ... arrow 50 ... volume diffraction grating 71 ... calibrator 51 ... calibration beam 72 ... calibration Light beam 52 ... light return facility 73 ... birefringent plate 53 ... lens 74 ... polarization 54 ... mirror 75 ... polarization 57 ... cylindrical lens 76 ... half-wave plate 58 ... parallel plate 77 ... 稜鏡 60 ... dispersion compensator 77a ... Body diffraction grating 61 ... Optical fiber 78 ... Half-wave plate 62 ... Optical phase effector 82 ...… 63 ... Entry window 86 ... Circulator

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Claims (1)

594082 Scope of patent application: 1. An optical dispersion compensator, which is used to make the performance of optical communication systems better, including: A calibration facility that receives a 5-dimensional end of an optical fiber from one of the optical communication systems and contains Spatially divergent beams of light of multiple frequencies, the calibration facility also transforms the spatially divergent beams into the main beams that are emitted thereby; an optical phase effector with an entrance window for receiving from the calibration The main collimated beam of the facility, and the received beam angle 10 is dispersed into a band pattern for transmission by the optical phase effect, whereby the received light is divided into a plurality of bands, giving a specific Light of a specific frequency in one of the wave bands is angularly deviated from light of different frequencies in the same wave band; and a light returning facility is received by the optical phase effects of the 15 band types of the angular dispersion of the The light and reflect it back through the optical phase effector to leave the optical phase effecter near the entrance window. 2. The compensator according to item 1 of the scope of patent application, wherein the main collimated light beam of the light emitted by the calibration facility has a divergence, which ensures that the main collimated light beam of the light striking the entrance window More than 50% of the energy is diffracted into less than three diffraction orders by any light beam with a specific wavelength of light scattered at an angle by an optical phase effector that becomes a band type. 3. The compensator described in item 1 of the scope of patent application, wherein light enters the optical phase effector through the 30 594082 entrance window at a near normal incidence angle. 4. The compensator according to item 1 of the scope of patent application, wherein the entrance window of the optical phase effector is at least partially transparent to the light impinging thereon. 5 5. The compensator according to item 1 of the scope of patent application, wherein the light returning facility includes a light focusing facility and a mirror disposed near a focal plane of the light focusing facility, the light focusing facility having The phase effect is projected onto the mirror by the angularly dispersed rays of the radiating band type. The mirror reflects the light impinging on it back to the light focusing facility in the direction of 10 directions. 6. The compensator according to item 5 of the scope of patent application, wherein the light focusing device is projected to a different position of each band of the band pattern of the light scattered at an angle by the optical phase effector on the mirror . 7. The compensator according to item 5 of the scope of patent application, wherein the distance between the light focusing device and the optical phase effector is adjustable. 8. The compensator according to item 5 of the scope of patent application, wherein the mirror is a curved surface. 9. The compensator according to item 8 of the scope of patent application, wherein the curvature of the mirror is adjustable. 20 10. The compensator according to item 9 of the scope of patent application, wherein the curvature of the mirror is adjustable by bending the mirror. 11. The compensator according to item 10 of the scope of patent application, wherein the force for bending the mirror is selected from the group consisting of mechanical, electrical, magnetic, and thermal. 31 594082 12. As claimed, the patent has a heavy curvature, B, in which the mirror has multiple revolutions and the curvature of the mirror is compensated by Pingjiang as described in item 9 of the scope of patent application. 5 and the curvature of the mirror is adjusted by swapping the mirror. Where the mirror is a substitute for another mirror with a different curvature = it is made of a rrfl item compensator, where the optical phase port is made of a material plate on the surface, and the light enters the tunnel to enter the pre-learning phase effect The reflector is formed on the outer surface of the plate after the device, and the entrance window system 10 15 · is a compensator as described in the scope of application for patent application, wherein the entrance window system is made with the chamfered edge of the plate. 16. The compensator according to item 14 of the scope of patent application, wherein the entrance window is made of-稜鏡, which is extended from two parallel surfaces of the silk phase effect device, and enters the optical phase through the entrance window. The light from the effector is reflected by the interior of the ridge before hitting one of the two parallel surfaces. 17. As claimed in the scope of patent application; [4] The compensator described in [4], wherein one of the two parallel surfaces of the optical phase effector is partially transparent, so that a part of the light impinging on it leaves the optical phase effector. . 20 18. The compensator according to item 17 of the scope of patent application, wherein the light radiated by the optical phase effector through the partially transparent surface is refracted by an angle exceeding 45 ° by the normal. 19. The compensator according to item 1 of the scope of patent application, wherein the optical phase effect is made of a material having a refractive index greater than that of a medium surrounding the optical phase effector. 32 594082 20. —A method for optical dispersion compensation, which is suitable for making the performance of optical communication systems better, including the steps of: radiating from the end of an optical fiber included in an optical communication system containing several frequencies The spatially divergent beam is calibrated as a main beam to be calibrated; the main calibration beam is angularly dispersed in an optical phase effector into a band pattern radiated by the optical phase effector, whereby the main calibration beam becomes Separation into multiple bands, such that light having a particular frequency in a particular band is deviated angularly from 10 rays of other frequencies in the same band; and reflecting the angularly scattered light back through the An optical phase effector to leave the optical phase effector near the entrance window. 21. The method as described in item 20 of the scope of patent application, wherein the mainly collimated beam of light radiated by the calibration facility has a divergence, which ensures that 15 of the collimated beam of light colliding with the entrance window More than 50% of the energy has a beam with a specific wavelength of light scattered at an angle emitted by an optical phase effect device in the form of a band, diffracted into less than three diffraction orders. 22. The method according to item 20 of the scope of patent application, wherein the light returning device 20 includes a light focusing facility and a mirror disposed near a focal plane of the light focusing facility, comprising the steps of: focusing the light The facility collects light scattered at an angle by the optical phase effector's radiated band pattern for projection onto the mirror; and 33 594082 the mirror reflects the light impinging on it back towards the light focusing facility . 23. The method according to item 22 of the scope of patent application, wherein the light focusing device is projected to a different position of each band of the band-type light of the light scattered by an angle of 5 by the optical phase effect produced on the mirror . 24. The method according to item 22 of the scope of the patent application, further comprising the step of adjusting the distance between the light focusing device and the optical phase effect device. 25. The method described in item 22 of the scope of patent application, further comprising the step of adjusting the curvature of the mirror. 10 26. The method of claim 25, wherein the curvature of the mirror is adjustable by bending the mirror. 27. The method of claim 26, wherein the force for bending the mirror is selected from the group consisting of mechanical, electrical, magnetic, and thermal. 15 28. The method according to item 25 of the scope of patent application, wherein the mirror has multiple curvatures, and the curvature of the mirror is adjusted by translating the mirror. 29. The method as described in claim 25 of the scope of patent application, wherein the mirror is replaceable, and the curvature of the mirror is adjusted by replacing the mirror with another mirror having a different curvature. 20 30. The method according to item 20 of the scope of patent application, wherein the light radiated from the optical phase effect device through the partially transparent surface is refracted by an angle exceeding 45 ° by the normal.